According to the Third Generation Partnership Project (3GPP) specifications for wireless communication systems (Release 8 and later Releases), a Long Term Evolution (LTE) cellular radio communication system uses Orthogonal Frequency Division Multiple Access (OFDM) as a multiple access technique (called OFDMA) in the downlink (DL) from network nodes (evolved NodeBs, or eNodeBs) to user equipments (UEs) and Discrete Fourier Transform (DFT)-spread OFDM in the uplink (UL) from UEs to eNBs. The LTE specifications can be seen as an evolution of current wideband code division multiple access (WCDMA) system specifications. An LTE system is sometimes also called an Evolved Universal Terrestrial Radio Access (E-UTRA) communication system.
WCDMA communication system channels are described in 3GPP Technical Specification (TS) 25.211 V8.6.0, Physical Channels and Mapping of Transport Channels onto Physical Channels (FDD) (Release 8) (December 2009) and other specifications. For example, a high speed downlink shared channel (HS-DSCH) carries paging messages, among other information.
LTE communication channels are described in 3GPP TS 36.211 V9.1.0, Physical Channels and Modulation (Release 9) (December 2009) and other specifications. For example, control information exchanged by eNodeBs and UEs is conveyed by physical uplink control channels (PUCCHs) and by physical downlink control channel (PDCCHs). In an OFDMA communication system, a data stream to be transmitted is portioned among a number of narrowband subcarriers that are transmitted in parallel. In general, a physical resource block is a particular number of particular subcarriers used for a particular period of time. Different groups of subcarriers can be used at different times for different purposes and different users. OFDMA communication systems are described in the literature, for example, U.S. Patent Application Publication No. US 2008/0031368 A1 by B. Lindoff et al.
3GPP TS 25.331 V8.9.0, Radio Resource Control (RRC), Protocol Specification (Release 8) (December 2009) specifies an RRC protocol for the radio interface between a UE and a radio access network (RAN) that includes NodeBs and Radio Network Controllers in WCDMA communication systems, and 3GPP TS 36.331 V8.8.0, Radio Resource Control (RRC), Protocol Specification (Release 8) (December 2009) specifies the RRC protocol for the radio interface between a UE and a RAN that includes eNodeBs in LTE and other communication systems. The current RRC protocol specifies RRC procedures, including RRC state transitions and a Fast Dormancy procedure that enables UEs that are “connected all the time” to save battery power. An RRC connection is a point-to-point bi-directional connection between RRC peer entities in the UE and RAN that is characterized by the allocation of a radio network temporary identifier.
A UE has either zero or one RRC connection that can include several signaling connections. A UE is in a “Connected mode” state when the UE is switched on and with an RRC connection established, and the UE is in an “Idle mode” state when the UE is switched on and without an RRC connection established. In a WCDMA communication system, the “Connected mode” states currently specified by 3GPP TS 25.331 are denoted CELL_PCH, URA_PCH, CELL_FACH and CELL_DCH. In an LTE system, the only “Connected mode” state currently specified by 3GPP TS 36.331 is denoted RRC_CONNECTED.
FIG. 1 illustrates a user plane of an exemplary LTE cellular communication system 100 that includes UEs 110, 120, a RAN that includes a plurality of eNodeBs 130-1, 130-2, . . . , 130-N, and a core network (CN) that includes a serving gateway (SGW) node 140 and a packet data network 150. Other nodes can also be provided in the system 100.
Each eNodeB 130-1, 130-2, . . . , 130-N serves a respective geographical area that is divided into one or more cells. An eNodeB can use one or more antennas at one or more sites to transmit information into its cell(s), and different antennas can transmit respective, different pilot and other signals. Neighboring eNodeBs are coupled to each other by an X2-protocol interface that supports active-mode mobility of the UEs. An eNodeB controls various radio network functions, including for example single-cell radio resource management (RRM), such as radio access bearer setup, handover, UE UL/DL scheduling, etc. Multi-cell RRM functions can also use the X2-protocol interfaces. Each eNodeB also carries out the Layer-1 functions of coding, decoding, modulating, demodulating, interleaving, de-interleaving, etc.; and the Layer-2 retransmission mechanisms, such as hybrid automatic repeat request (HARQ), and functions of radio link control (RLC) and RRC. The eNodeBs 130-1, 130-2, . . . , 130-N are coupled to one or more SGWs 140 (only one of which is shown in FIG. 1).
From the point of view of a control plane of the example LTE communication system 100, LTE-Uu protocol interfaces couple the UEs 110, 120 to the eNodeBs 130, and S1-MME protocol interfaces couple the eNodeBs 130 to a Mobility Management Entity (MME), which is a name for an SGW 140 in the control plane. In general, the LTE-Uu interface provides control-plane signaling between a UE and the RAN according to 3GPP TS 36.331.
UEs 110, 120 are generally wireless communication devices, such as cellular radiotelephones, personal digital assistants (PDAs), Personal Communications System (PCS) terminals, laptop computers, palmtop computers, or any other type of device or appliance that includes a communication transceiver that permits the device to communicate with other devices via a wireless link. A PCS terminal can combine a cellular radiotelephone with data processing, and facsimile and data communication capabilities. A PDA can include a radiotelephone, a pager, an Internet/intranet access device, a web browser, an organizer, calendars, and/or a global positioning system (GPS) receiver. One or more of UEs 110, 120 can be referred to as a “pervasive computing” device. In some implementations, the UEs 110, 120 can include wireline telephones (e.g., Plain Old Telephone system (POTs) telephones) that are connected to a Public Switched Telephone Network (PSTN). In any event, the UEs 110, 120 carry out the appropriate functions of Layers 1-3 etc. in cooperation with the eNodeBs.
The network 100 can exchange information with one or more other networks of any type, including a local area network (LAN); a wide area network (WAN); a metropolitan area network; a telephone network, such as a public switched terminal network or a public land mobile network; a satellite network; an intranet; the Internet; or a combination of networks. It will be appreciated that the number of nodes illustrated in FIG. 1 is purely exemplary. Other configurations with more, fewer, or a different arrangement of nodes can be implemented. Moreover, one or more nodes in FIG. 1 can perform one or more of the tasks described as being performed by one or more other nodes in FIG. 1. For example, parts of the functionality of the eNodeBs can be divided among one or more base stations and one or more radio network controllers, and other functionalities can be moved to other nodes in the network.
According to subclause 8.1.13 of 3GPP 25.331, for example, a signaling connection release procedure is used to notify the UE that one of its RRC signaling connections has been released. The procedure is initiated by RAN transmission of a release message on a DL dedicated control channel (DCCH), and in response to the message, the UE indicates the release by transmission of an UL indicator message as specified in subclause 8.1.14 of 3GPP 25.331.
FIG. 2 illustrates the signaling connection release indication procedure specified by subclause 8.1.14 of 3GPP TS 25.331 that is used by the UE to indicate to the RAN that one of its signaling connections has been released or to request the RAN to initiate a state transition to a battery-efficient RRC state. Such an indicator, or request, is sometimes called a “fast dormancy” request, and in response to such an UL indicator message, the RAN can send a DL message that reconfigures the UE to a more power-efficient state. If the UE does not send such a “fast dormancy” request, the UE typically remains in a less power-efficient state for a longer time, depending for example on network implementation (e.g., whether the network includes a UE inactivity timer).
As specified by subclause 8.1.14.2 of 3GPP 25.331, for example, the network can restrict the frequency of a UE's transmitting signaling connection release indications, and thus “fast dormancy” requests, by broadcasting a prohibit timer (which is called T323 in 3GPP TS 25.331). The timer is started when the UE transmits a signaling connection release indicator with a cause value, and while the timer is running, the UE is inhibited from sending further signaling connection release indicators with a cause value corresponding to UE-requested packet-switched data session end. The frequency of signaling connection release indicators can also be limited by a counter, e.g., a total number of permitted requests in a state, such as the CELL/URA_PCH state. The frequency of signaling connection release indicators can also be limited by prohibiting transmission of signaling connection release indicators with a cause value if the discontinuous reception (DRX) cycle of the URA_PCH state or CELL_PCH state is long enough that the URA_PCH state or CELL_PCH state can be considered to be battery-efficient.
Even if the DRX cycle in the URA_PCH state or CELL_PCH state is long enough for the state to be considered battery-efficient, however, a mobile UE can be required to send more CELL or URA updates in the CELL_PCH or URA_PCH states than it is in RRC Idle mode. Current ways to limit the signaling load do not consider this aspect, as the Fast Dormancy procedure specified in 3GPP TS 25.331, for example, does not distinguish the DRX settings and mobility while the UE is in the URA_PCH state or CELL_PCH state. Thus, under some conditions the UE can uselessly request Fast Dormancy (and waste power doing so) while the network decides to keep the UE in the CELL_PCH state or URA_PCH state because it is considered battery-efficient.